It has been recognized that trace elements, such as chromium, iron, zinc, copper, phosphorous, manganese and magnesium, have benefit as a dietary supplement for animal and poultry feeds. For example, trivalent chromium is a known cofactor with insulin; together they metabolize carbohydrates and glucose particularly during stress, such as heat, birth or transport, and during the early growth phases. Adequate dietary intake of zinc in animal and poultry is recognized as preventing skin conditions and providing healthy growth and increased weight. It is also recognized that iron is essential to the elementary metabolic process in the cell in preventing iron-deficiency anemia.
If the trace metals are merely added to the animal feed as an inorganic salt, a substantial portion of the metal is passed through the animal with the manure and urine and the nutrient deficiency problems remain unsolved. With large animal feed lots, the disposal of manure containing large amounts of trace elements can be a severe environmental problem.
In order to increase the biological availability of trace metals, it has been proposed to utilize the metals as amino acid metal proteinates or complexes. Not only does the proteinate render the metal more available to the biochemical system of the animal, but also reduces the amount of metal that is passed through the animal as manure. For example, U.S. Pat. No. 5,278,329 is directed to a metal complex of methionine to be used as an animal feed, while U.S. Pat. No. 5,948,772 is directed to a dietary feed supplement consisting of chromium tripicolinate. Not previously realized, however, is the extent to which leather scrap can be used to prepare such proteinates or complexes. In fact, prior efforts have been directed to the removal of complexed metals.
Chromium leather waste consists of chromium-tanned, unfinished leather shavings, trimmings and/or fleshings. In the past, the chrome leather waste was merely discarded to a landfill, but U.S. Pat. No. 4,100,154 describes a method of converting chrome leather waste into a protein hydrolysate and for recovering chromium compounds from the waste. In accordance with the aforementioned patent, the leather waste is heated in an aqueous solution of an alkali material, such as calcium oxide or calcium hydroxide, for a period of time to sever the chromium linkages and dechrome the leather. Through this process, the original collagen of the leather is reduced to low molecular weights, thereby producing a water soluble protein hydrolysate and water insoluble chromium compounds. According to U.S. Pat. No. 4,100,154, the precipitated chromium compounds are separated from the protein hydrolysate and the hydrolysate can then be neutralized with acid to provide an animal feed supplement, while the chromium compounds are washed to remove residual protein and then dissolved in sulfuric acid to provide a water soluble chromium salt useful in tannery operations.
The invention is directed to a water soluble leather hydrolysate metal proteinate to be used as a feed nutrient and to a method of producing the metal proteinate. In accordance with the invention, chrome-tanned leather scrap and shavings are heated to a temperature generally in the range of 180xc2x0 F. to 200xc2x0 F. in an aqueous medium containing an alkali material to hydrolyze the leather scrap and produce a protein hydrolysate along with insoluble chromium compounds. The hydrolyzation reduces the chromium content of the hydrolysate to a value less than 10 ppm of chromium, and the hydrolysate includes a mixture of amino acids with hydroxyproline, aspartic, glycine, proline, glutamic and alanine being the most prevalent acids.
The insoluble chromium compounds are separated by filtration from the hydrolysate. The hydrolysate is carbonated for calcium removal and is then concentrated by evaporation to an approximate 50% solid solution. Following this, an oxidizing material, such as hydrogen peroxide, is added to the hydrolysate to oxidize and eliminate any undesirable trace organics that may remain from the leather tanning operation. After oxidation, a water soluble salt of a di- or tri-valent metal, such as trivalent chromium, iron, manganese, copper, zinc or magnesium is added to the hydrolysate and mixed therewith, preferably by a high shear mixer, to provide a metal hydrolysate proteinate. It is believed that aspartic acid and glutamic acid are the primary agents in chelating, as they have two available sites that accept divalent metals, such as zinc, iron, and the like.
The leather hydrolysate metal proteinate has particular use as a nutrient for animals, poultry and for aquaculture, and provides precise pre-selected control over the assimilation of the metal into the biological system of the animal.
As the metal is present as a hydrolysate proteinate , the bio-availability of the metal is increased and the output of the metal in manure or waste products is reduced thereby decreasing the environmental problem of waste disposal.
Various other features, objects and advantages of the invention will be made apparent from the following description.